Safety, defined as the frequency and severity of vaccine-related reactogenicity events and reported AEs [ Time Frame: Throughout trial (reactogenicity for 7 days following each vaccination) ] [ Designated as safety issue: No ]

Immunogenicity (humoral) defined by H5 HAI titer [ Time Frame: At all available timepoints ] [ Designated as safety issue: No ]

The purpose of this study is to compare the safety and immunogenicity over a 9-month period of five different dosages of Ad4-H5-Vtn in volunteers (Vaccinees) who receive three doses of the study vaccine or placebo. In addition, transmission of Ad4-H5-Vtn will be evaluated in all Household Contacts residing with the vaccinated volunteers.

Vaccinees also may participate in a substudy in which they receive a booster vaccination with the licensed Influenza Virus Vaccine, H5N1 (Sanofi Pasteur).

Detailed Description

At least 160 healthy Vaccinees will be randomized into 5 ascending dosage cohorts each consisting of at least 32 volunteers. In each dosage cohort Vaccinees will be randomly assigned to receive 3 doses of either Ad4-H5-Vtn or placebo separated by approximately 56 days. Volunteers will be followed for 168 days post-third vaccination.